Swiss Ephemeris API

Swiss Ephemeris - de facto standard for astronomical calculations in astrology: most serious software relies on it, including Astrodienst (astro.com), Solar Fire, Kerykeion. It reads ephemerides DE431 from NASA JPL and provides subsecond accuracy. AstroWay API gives direct HTTP access to it - without compiling C libraries, without downloading .se1 files, without memory management. One POST request, JSON in response.

Why Swiss Ephemeris through API

Self-hosting Swiss Ephemeris means: gathering C libraries (or WASM build), placing several hundred megabytes of .se1 files, keeping them up-to-date, and implementing house cusps, aspects, phases yourself. Through API, all this is a foreign hassle:

• Zero infrastructure: no binaries, ephemeris files, or cold-start delays. Calculation is performed server-side on the same engine as Astrodienst.
• Subsecond accuracy: < 0.1″ against the reference swetest CGI from Astrodienst, verified on 873 frozen snapshot tests at each deploy.
• Full date range: DE431 covers 13201 BCE – 17191 CE, so historical and distant future charts are calculated without loss of accuracy.
• Not just positions: ephemeris data immediately available for house cusps (15 systems), aspects, eclipses, transits, progressions - what you’d have to write yourself in self-host.

Wskazówka

Accuracy is triangulated against three independent sources (swetest CGI, Kerykeion, Prokerala) + against NASA 5-Millennium Eclipse Catalog. Details and numbers - on the page Accuracy of calculations.

What Swiss Ephemeris calculates

Endpoint	Credits	What returns
/v1/chart	20	Full chart: planets + houses + aspects
/v1/planets	10	Geocentric positions of planets (longitude, latitude, speed, retrograde)
/v1/houses	10	House cusps - 15 systems (Placidus, Koch, Whole Sign, Equal…)
/v1/transits	50	Transits to natal chart on given date
/v1/progressions	50	Secondary progressions (day = year)
/v1/eclipses	100	Solar and lunar eclipses (verified vs NASA Catalog)
/v1/moon-phase	10	Moon phase, illumination, next quarter
/v1/fixed-stars	20	Conjunctions of planets with fixed stars

This is part of 760 endpoints of the platform - full list in API documentation.

Example

cURL

curl -X POST https://api.astroway.info/v1/planets \
  -H "X-Api-Key: aw_live_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "date": "1990-07-14",
    "time": "14:30:00",
    "timezoneOffset": 3,
    "latitude": 50.4501,
    "longitude": 30.5234
  }'

Node.js

const r = await fetch('https://api.astroway.info/v1/planets', {
  method: 'POST',
  headers: {
    'X-Api-Key': process.env.ASTROWAY_API_KEY!,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    date: '1990-07-14',
    time: '14:30:00',
    timezoneOffset: 3,
    latitude: 50.4501,
    longitude: 30.5234,
  }),
});
const { data } = await r.json();
const sun = data.planets.find((p) => p.name === 'Sun');
console.log(`Sun: ${sun.longitude.toFixed(4)}° retrograde: ${sun.isRetrograde}`);

Python

import os, requests

r = requests.post(
    'https://api.astroway.info/v1/planets',
    headers={'X-Api-Key': os.environ['ASTROWAY_API_KEY'], 'Content-Type': 'application/json'},
    json={
        'date': '1990-07-14',
        'time': '14:30:00',
        'timezoneOffset': 3,
        'latitude': 50.4501,
        'longitude': 30.5234,
    },
)
data = r.json()['data']
sun = next(p for p in data['planets'] if p['name'] == 'Sun')
print(f"Sun: {sun['longitude']:.4f}° retrograde: {sun['isRetrograde']}")

Who uses it

• Astro application developers: subsecond positions without self-host C libraries
• AI agents: accurate ephemerides as grounding for LLM (through MCP server)
• Researchers: mass calculations on historical DE431 date range
• Migration from self-host: replacing local swisseph with HTTP without loss of accuracy

Pricing

Positions of planets (/v1/planets) - 10 credits, full chart (/v1/chart) - 20. On Free tariff (760+ endpoints, 10,000 credits/month) - approximately 1,000 planet queries per month for free, without card.

Accuracy of calculations → Triangulation, NASA validation, snapshot tests

Quick start First request in 5 minutes

Tariffs From free to Enterprise